Cleaning process

ABSTRACT

The present invention is directed to a process for cleaning a cleaning object, comprising the steps of: placing water and organic substances containing a nonionic surfactant composition having a cloud point of not higher than 100° C. in a ratio of not less than 30% by weight, with or without previous blending, in a cleaning vessel, wherein the organic substances have a specific gravity higher than that of water and, when mixed with water, placed in the cleaning vessel and kept standing at a temperature of from 20° to 100° C. for 30 minutes, exhibit phase separation such that not less than 50% by weight of the organic substances is separated into a lower layer; maintaining a temperature above the cloud point of the nonionic surfactant, thereby allowing water and the organic substances to be in the state of phase separation in which the concentration of the organic substances in a lower layer is higher than that in an upper layer; and cleaning the cleaning object in the lower layer.

TECHNICAL FIELD

The present invention relates to a process for cleaning solid surfacesof glass, ceramics, metals, plastics, etc. Specifically, the presentinvention relates to a process for cleaning machine parts, electronicparts, precision parts, machine tools used for assembling or processingthese parts, or the like, which are stained with fats and oils, machineoils, quenching oils, greases, cutting oils or other working oils,waxes, liquid crystals, fluxes, abrasion dusts, cutting dusts, or thelike. More specifically, it relates to a process for cleaning wherein adense detergent component with a high cleaning performance can be usedwithout concern about fire, explosion and workplace environmentpollution due to odor, etc.

BACKGROUND ART

Conventionally, chlorine-based solvents such as 1,1,1-trichloroethaneand tetrachloroethylene, and chlorofluorocarbon solvents such astrichlorotrifluoroethane have been used for cleaning solid surfaces ofglass, ceramics, metals, plastics, etc., e.g., surfaces of machineparts, electronic parts, precision parts, machine tools used forassembling or processing these parts, which are stained with fats andoils, machine oils, quenching oils, greases, cutting oils or otherworking oils, waxes, liquid crystals, fluxes, abrasion dusts, cuttingdusts, or the like, because these solvents have a high cleaningperformance and are easy to handle. Here, these parts and tools arecollectively referred to as "machine and precision parts."

The use of detergents containing chlorofluorocarbon- or chlorine-basedsolvents is being reconsidered or totally banned or legally regulated,as they have proven to be potentially hazardous to the globalenvironment and human life, due to ozone layer depletion,carcinogenesis, etc. caused by atmospheric evaporation or diffusion ofthe solvents, or subterranean water contamination therewith.

In response to this trend, various detergents or cleaning technologiesthat can replace such chlorofluorocarbon- or chlorine-based detergentshave already been proposed. Typical examples include

1) the method using a hydrocarbon solvent, such as kerosene, toluene,xylene or petroleum solvent, or a detergent comprising such ahydrocarbon solvent and an appropriate amount of surfactant (JapanesePatent Laid-Open No. 3-94082);

2) the method using a glycol, a liquid nonionic surfactant of lowviscosity, or a dense detergent liquid comprising such a substance and asmall amount of water (Japanese Patent Laid-Open Nos. 3-62895 and3-162496); and

3) the method using a detergent containing a surfactant and builder, thedetergent being diluted with a large amount of water. However, all thesecleaning methods are problematic as to a cleaning performance, cleaningworkplace environmental protection and other factors.

For example, the cleaning methods 1) and 2) described above use acleaning liquid wherein organic substances form a continuous phase.These methods exhibit an excellent cleaning performance against varioustypes of organic stains including liquid organic substances, such asmachine oils and metallurgic oils, and viscous or solid organicsubstances, such as grease and fluxes. Such an excellent cleaningperformance of these methods may be explained by the cleaning mechanismof the detergents. Specifically, organic stains are removed bydissolving into the cleaning liquid, since the organic substances form acontinuous phase in the cleaning liquid as in the case ofchlorofluorocarbon-based solvents and 1,1,1-trichloroethane. However,the cleaning methods 1) and 2) have risks of catching fire, exploding,and polluting workplace environment due to evaporation of volatileorganic components, such as hydrocarbon solvents and glycols, becauseorganic substances form a continuous phase. Detergents containing anappropriate, small amount of water to prevent catching fire have no riskof fire, provided that the water content is appropriately controlled atthe time of cleaning. However, these detergents need extra cost andpersonnel for controlling water content, i.e., analytical instrument andwater supply facilities for controlling water, and personnel for theiroperation. In addition, the other problem, workplace environmentalpollution due to evaporation of organic components remains unsolved.

Also, method 3), which uses a detergent containing a surfactant andbuilder, the detergent being diluted with a large amount of water, isdesirable from the viewpoint of workplace environmental protection,because there is no risk of catching fire and pollution of workplaceenvironment due to evaporation of organic components. However, unlikethe cleaning methods 1) and 2), method 3) uses a cleaning liquid whereinwater forms a continuous phase. In this method, cleaning is performed bya cleaning mechanism that the surfactant in water is adsorbed to theparts being cleaned or organic stains adhering thereon, and decreasestheir interfacial tensions to promote their self-aggregation, therebyallowing the aggregated organic stain to be removed by rolling-upmotion. As compared with methods 1) and 2) in which organic stains areremoved by dissolving into a detergent liquid, method 3) is considerablyinferior in a cleaning performance against viscous grease and solidstains, such as fluxes and waxes.

In this situation, there is need for a new cleaning method which showsboth an excellent cleaning performance against organic stains of variousproperties, as obtained with the detergents based on the dissolutionmechanism in methods 1) and 2), and excellent properties for ensuringcleaning workplace safety, such as nonflammability and low volatility,as obtained with detergents diluted with water as exemplified by method3).

EP-A-0466054 and EP-A-0535689 disclose methods for improving treatmentefficiency of waste liquid by a detergent having a particular cloudpoint.

FR-A-2146633 and JP-A-2034683 disclose methods for cleaning in a stateof phase-separation of cleaning liquid, wherein the cleaning is carriedout in the lower organic solvent phase.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a cleaning processwhich achieves both an excellent cleaning performance against organicstains of various properties, and high safety in cleaning workplace,including nonflammability and low volatility.

In order to achieve the above object, the present inventors madeextensive investigation, and found that an excellent cleaningperformance and high safety in workplace environment can be achieved bythe following cleaning process comprising the steps of:

placing water and organic substances, with or without previous blending,in a cleaning vessel, the organic substances having a specific gravityhigher than that of water and being capable of exhibiting phaseseparation to water;

allowing water and the organic substances to be in the state of phaseseparation in which the concentration of the organic substances in alower layer is higher than that in an upper layer; and cleaning acleaning object in the lower layer. An excellent cleaning performancecan be obtained because this method allows the cleaning object to be incontact with the dense liquid of organic substances which form the oilphase as the lower layer, and high workplace safety is achieved becausethe upper water layer prevents the organic substances from evaporatingand catching fire. Based upon these findings, the inventors made furtherinvestigations, and developed the present invention.

Specifically, the present invention is concerned with the followings:

(1) A process for cleaning a cleaning object, comprising the steps of:

placing water and organic substances, with or without previous blending,in a cleaning vessel, the organic substances having a specific gravityhigher than that of water and being capable of exhibiting phaseseparation to water;

allowing water and the organic substances to be in the state of phaseseparation in which the concentration of the organic substances in alower layer is higher than that in an upper layer; and

cleaning the cleaning object in the lower layer;

(2) The process for cleaning described in (1) above, wherein ultrasonicwave, stirring or in-liquid jetting is applied to the upper and/or lowerlayers;

(3) The process for cleaning described in (1) or (2) above, wherein thecleaning object is pulled up from the upper layer and then rinsed byjetting or spraying water in a space above the upper layer;

(4) The process for cleaning described in any one of (1) to (3) above,wherein the organic substances, when mixed with water, placed in thecleaning vessel and kept standing at a temperature of from 20° to 100°C. for 30 minutes, exhibit phase separation such that not less than 50%by weight of the organic substances is separated into the lower layer;

(5) The process for cleaning described in (4) above, wherein 80 to 99.9%by weight of the organic substances is separated into the lower layer;

(6) The process for cleaning described in any one of (1) to (5) above,wherein main components of the organic substances are one or more kindsselected from the group consisting of nonionic surfactants; aromatichydrocarbon compounds; and esters, ethers, alcohols and ketones, eachhaving an aromatic hydrocarbon group;

(7) The process for cleaning described in any one of (1) to (6) above,wherein the organic substances contain a nonionic surfactant having acloud point of not higher than 100° C. in a ratio of not less than 30%by weight; and

(8) The process for cleaning described in (7) above, wherein thenonionic surfactant having a cloud point of not higher than 100° C. is acompound represented by the formula:

    R.sub.1 X(AO).sub.m R.sub.2 or R.sub.1 X(AO).sub.n YR.sub.2

wherein R₁ represents a hydrocarbon group having 6 to 18 carbon atomsthat may have a substituent and that has at least one aromatic ring; R₂represents a hydrogen atom or a hydrocarbon group having 1 to 10 carbonatoms that may have a substituent; X represents an ether group, an estergroup or an amino group; Y represents an ether group or an ester group;(AO) represents an alkylene oxide having 2 to 4 carbon atoms; m and nare average molar addition numbers of (AO), m being 0 to 20 and n being1 to 20.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic diagram of the cleaning vessel of a cleaningapparatus used for the cleaning process of the present invention, inwhich the numerical symbols represent the following: 1, work piece; 2,jetting nozzle; 3, pump; 4, recycle treatment devise; 5, ultrasonicoscillator.

BEST MODE FOR CARRYING OUT THE INVENTION

The cleaning process of the present invention is characterized in thatwater and organic substances whose specific gravity, as a whole, ishigher than that of water and which are, as a whole, capable ofexhibiting phase separation to water are placed in a cleaning vessel,with or without previous blending (the thus-obtained mixture ishereinafter referred to as "cleaning liquid"), and the cleaning objectis cleaned in the lower layer, while the cleaning liquid is in the stateof phase separation in which the organic substance concentration in thelower layer is higher than that in the upper layer.

Accordingly, any cleaning liquid can be used as long as it compriseswater and organic substances having a specific gravity higher than thatof water and being capable of exhibiting phase separation to water, andshows phase separation such that the organic substance concentration inthe lower layer (oil phase) is higher than that in the upper layer(water phase) when they are placed in a cleaning vessel with or withoutprevious blending.

Preferred examples of the organic substances include compounds having aspecific gravity of not less than 1.000 at 20° C. Although these organiccompounds may or may not contain halogen atoms, halogen-free organicsubstances are preferred to halogen-containing compounds, such asfluorine compounds e.g., hydrochlorofluorocarbon (HCFC),hydrofluorocarbon (HFC)!, chlorine compounds (e.g., chlorinatedparaffin, trichloroethylene) and bromine compounds (e.g., bromobenzene,bromoether benzene), from the viewpoint of environmental protection,safety and other factors.

Accordingly, suitably useful organic substances containing no halogenatoms mainly contain one or more substances selected from the groupconsisting of nonionic surfactants; aromatic hydrocarbon compounds; andesters, ethers, alcohols and ketones, each having an aromatichydrocarbon group.

More specifically, compounds consisting of plural elements selected fromcarbon, hydrogen, oxygen and nitrogen are useful. Such compounds includeketones such as dimethoxyphenylacetone and acetophenone; epoxides, suchas styrene oxide, phenyl glycidyl ether, glycidol, polypropyleneglycoldiglycidyl ether, ethyleneglycol diglycidyl ether and neopentylglycoldiglycidyl ether; esters, such as triallyl trimellitate,tetrahydrofurfuryl acrylate, trimethylolpropane triacrylate, butanedioldiacrylate, benzyl methacrylate, methyl salicylate, diethyl phthalate,dibutyl phthalate, dimethyl adipate, dimethyl malate, tributyl citrate,tributyl trimellitate and benzyl benzoate; alcohols, such asphenoxyethanol, butylcatechol, 1,4-butanediol, isoeugenol, cinnamicalcohol, benzyl alcohol and dibenzylphenol; polyalkylene glycols, suchas polypropylene glycol and polypropylene polyethylene copolymer;ethers, such as dibenzyl ether; and hydroxyethylpiperazine,epichlorohydrin, anisaldehyde, phenyl ethyl acetal, and ester, ketoneand alkylene oxide derivatives thereof.

Preferable glycol ethers are polypropylene glycol, polypropylenepolyethylene copolymer and other polyalkylene glycols having a molaraddition number of 3 to 50, and alkyl ethers and alkyl esters thereof.

Organic substances containing halogen atoms include compounds obtainedby replacement of some or all of the hydrogen atoms with halogen atoms,the hydrogen atoms being bound to the carbon atoms of chainhydrocarbons; aromatic or alicyclic hydrocarbons; hydrocarbonscontaining an aromatic or alicyclic hydrocarbon; alcohols, fatty acids,and amines, each being derived therefrom; ethers, esters, ketones, andamides, each resulting from reaction each other; and ethylene oxides,propylene oxides and other alkylene oxide adducts of these alcohols,fatty acids and amines.

Examples of compounds obtained by replacement of some or all of thehydrogen atoms with halogen atoms, the hydrogen atoms being bound to thecarbon atoms of chain hydrocarbons, aromatic or alicyclic hydrocarbons,or hydrocarbons containing an aromatic or alicyclic hydrocarbon includechlorocyclohexane, dichlorobenzyl, dichloroxylene, chlorotoluene,chlorinated naphthalene, bromobenzene, dibromobenzene, trichlorobenzene,fluorostyrene, fluorotoluene, 1,5-dichloropentane, 1,4-dibromobutane andoctyl bromide.

Examples of compounds obtained by replacement of some or all of thehydrogen atoms with halogen atoms, the hydrogen atoms being bound to thecarbon atoms of alcohols and fatty acids derived from chainhydrocarbons, aromatic or alicyclic hydrocarbons, or hydrocarbonscontaining an aromatic or alicyclic hydrocarbon; and ethers, esters, andketones, each resulting from reaction each other include chlorobenzylalcohol, 2,3-dibromo-1-propanol, fluorophenol, chlorophenol,dichlorophenol, p-chloroacetophenone, methyl o-bromobenzoate, ethyl2-bromoisobutyrate, decabromodiphenyl ether and α-bromobutyric acid.

Examples of organic substances containing halogen atoms also includecompounds synthesized by subjecting the OH group of chlorobenzylalcohol, 2,3-dibromo-1-propanol, fluorophenol, chlorophenol,dichlorophenol, or the like, to addition polymerization with ethyleneoxide or propylene oxide, provided that the above-mentioned propertiesof the cleaning liquid of the present invention are not affected.

The boiling point of the organic substances mentioned above ispreferably not less than 100° C. under atmospheric pressure, morepreferably not less than 150° C. This is because vaporization of thedetergent components during cleaning and drying steps should preferablybe avoided in view of protection of environment and workplaceatmosphere.

Any of these organic substances may be used singly or in combination.

In the present invention, it is preferable to use such organicsubstances containing a nonionic surfactant having a cloud point of nothigher than 100° C., more preferably not higher than 60° C., in a ratioof not less than 30% by weight, more preferably 50 to 100% by weight.

These compounds have specific temperature known as a cloud point; i.e.,they are soluble in water below a given temperature, because they havesuch a group as an ether group, an ester group or a hydroxyl grouptending to become hydrophilic through hydrogen bond, and are insolubleabove that temperature. It is therefore possible to form the two liquidlayers essential for the method of the present invention. Specifically,an upper layer water phase and a lower layer oil phase can be formed,simply by heating the cleaning liquid containing such organic substancesto a temperature above the cloud point, because the organic substanceseasily become insolubilized and separate in the cleaning liquid. Also,because the organic substances are soluble in water at temperaturesbelow the cloud point, the portion of cleaning liquid adhering to thecleaning object, such as machine parts, at the time of cleaning, caneasily be removed by rinsing with water at a temperature below the cloudpoint, so that the rinsing process is simplified.

In the present invention, from the viewpoint of degreasing ability andrinsability with water, preferred examples of the nonionic surfactanthaving a cloud point of not higher than 100° C. include a compoundrepresented by the formula:

    R.sub.1 X(AO).sub.m R.sub.2 or R.sub.1 X(AO).sub.n YR.sub.2

wherein R₁ represents a hydrocarbon group having 6 to 18 carbon atomsthat may have a substituent and that has at least one aromatic ring; R₂represents a hydrogen atom or a hydrocarbon group having 1 to 10 carbonatoms that may have a substituent; X represents an ether group, an estergroup or an amino group; Y represents an ether group or an ester group;(AO) represents an alkylene oxide having 2 to 4 carbon atoms; m and nare average molar addition numbers of (AO), m being 0 to 20 and n being1 to 20.

Among them, in cases where R₁ is a hydrocarbon group having 6 to 10carbon atoms and R₂ is a hydrogen atom, or a hydrocarbon group having 1to 2 carbon atoms, or a hydrocarbon group having an aromatic ring, it islikely that excellent phase separation and an oil phase of whichspecific gravity is higher than that of a water phase are obtained. Itis also preferable that m and n be 0 to 4 and 1 to 4, respectively, fromthe viewpoints of cleaning liquid viscosity and a cleaning performancein addition to the above features.

Examples of the compound represented by R₁ X(AO)_(m) R₂ or R₁ X(AO)_(n)YR₂ include ethylene oxide or propylene oxide adducts of phenol,styrenated phenol, benzylated phenol, cresol, benzyl alcohol orbenzylamine, and methyl esters and methyl ethers thereof. Specifically,such compounds include poly(average molar addition number P=1 to4)oxyethylene phenyl ether, poly(P=1 to 7)oxypropylene phenyl ether,poly(P=1 to 2)oxyethylene benzyl ether, poly(P=1 to 10)oxypropylenebenzyl ether, poly(P=2)oxyethylene/poly(P=4)oxypropylene phenyl etherand methyl or benzyl ethers thereof.

The cleaning liquid used for the method of the present invention mustexhibit phase separation such that a water phase is formed in the upperlayer and an oil phase in the lower layer. For efficiently and quicklyobtaining the two liquid layers, i.e., an upper layer water phase and alower layer oil phase, the ratio of organic substances transferring tothe lower layer of the cleaning liquid when the cleaning liquid is keptstanding at a temperature of 20° to 100° C. for 30 minutes (separationrate), is preferably not lower than 50% by weight, more preferably notlower than 80% by weight of the total organic substances. Higher organicsubstance separation rates are preferred, since the risk of fire andenvironmental pollution factors, such as odor, are reduced, because theamount of organic substances remaining in the water phase decreases.However, in view of rinsing efficiency after cleaning, the organicsubstances soluble to a certain extent in water are preferred; in thissense, it is preferable that the upper limit of separation rate is 99.9%by weight, more preferably 99% by weight.

Accordingly, in the method of the present invention, it is preferablethat when the organic substances are placed in a cleaning vessel afterblended with water and kept standing at a temperature of from 20° to100° C. for 30 minutes, the organic substances exhibit phase separationsuch that not less than 50% by weight, more preferably 80 to 99.9% byweight thereof is separated into the lower layer.

The term "organic substance" as used herein refers to a compound used asa detergent component and having a TOC (total organic carbon) value.Basically, TOC values can be determined by the method ofcombustion-infrared analysis described under "Total Organic Carbon(TOC)" in JIS-KO102 "Testing Methods for Industrial Waste Water", usingTOC-500 (manufactured by Shimadzu Corporation), for instance. Theorganic substance separation rate in the cleaning liquid, i.e., theratio of organic substances transferring to the lower layer of thecleaning liquid, as described above, is obtained by dividing the TOCvalue of the cleaning liquid in the lower layer by the sum of the TOCvalues of the cleaning liquids in the lower and upper layers, andmultiplying the quotient by a factor of 100, and is expressed in %values.

The cleaning liquid used in the present invention may optionally containvarious surfactants, organic or inorganic chelating agents, builders,silicone oil defoaming agents, amine rust preventives, antiseptics,alkanolamines (e.g., diethanolamine, methyldiethanolamine), alcohols,petroleum solvents, etc., in addition to the above-mentioned organicsubstances, as long as the essential properties of the cleaning liquidof the present invention are not lost. When a surfactant other than theabove-mentioned surfactants is used in the present invention, it ispreferable that the surfactant is a nonionic surfactant having anappropriate cloud point and a specific gravity of less than 1.000, whichis not likely to affect parts reliability for electric properties, orcause quality deterioration, such as rusting, because of the absence ofinorganic ions.

Examples of the optionally usable nonionic surfactants include ethertype surfactant such as alkyl ether, and alkyl allyl ether; alkyl estertype; amine-condensed type such as polyoxyalkylene alkylamine;amide-condensed type such as polyoxyalkylene alkylamide; Pluronic orTetronic types produced by random or block condensation ofpolyoxyethylene with polyoxypropylene; and polyethyleneimine-basedsurfactants.

The cleaning process of the present invention is characterized in thatthe above-described cleaning liquid is used to clean the cleaning objectin contact with the lower layer of the cleaning liquid, while thecleaning liquid is in phase separation such that the concentration ofthe organic substances in the lower layer is higher than that in theupper layer. The cleaning object, i.e., machine and precision parts, iscleaned by, for example, immersing the cleaning object in the lowerlayer for a given period of time. In this case, for obtaining asufficient cleaning performance, it is preferable that the entirecleaning object is in contact with the lower layer oil phase.Specifically, a better cleaning performance can be obtained, when thecleaning object is sufficiently immersed in the oil phase. Although theoil phase may be continuous or in the form of droplets, it is preferableto carry out cleaning, while a continuous oil phase is contained, fromthe viewpoint of both a cleaning performance and workplace environment.

FIG. 1 shows a schematic diagram of the cleaning vessel of a cleaningapparatus used for the cleaning process of the present invention. Abetter cleaning performance can be obtained, when a mechanical force orphysical force, such as ultrasonication, stirring or in-liquid jetting,is applied to the cleaning liquid during cleaning. FIG. 1 exemplifies acase in which each layer is stirred by circulating the water and oilphases using a pump (3). For protecting the workplace environment, it ispreferable that the mechanical force etc. be applied to the extent thatthe lower layer oil phase does not appear on the upper surface of theupper layer water phase, so that odor etc. can be suppressed.

It is preferable, from the viewpoint of cleaning efficiency that the oilphase depth in the cleaning vessel be set at a level such that theentire machine and precision parts are immersed. Also, the water phasedepth is set at a level such that the oil phase surface is fully coveredtherewith for maintaining a good workplace environment. However, it ispreferable that the depth be at least such that the entire machine andprecision parts can be almost immersed, when the water phase is used forrinsing. When the water phase is used for rinsing, it is preferable toapply a mechanical force or physical force, such as ultrasonication,stirring or in-liquid jetting, as in the case of cleaning in the oilphase. These means, e.g., ultrasonication and stirring, may be performedat the same time, and the water and oil phases may be so treated at thesame time.

It is preferable that oily or solid stains contaminating in the waterphase be removed using various separation devices, such as filters andoil-water separators, arranged in the circulatory system, so that abetter cleaning performance is ensured. Solid stains in the oil phasecan also be removed in the same manner as stains in the water phase.

In the present invention, the cleaning object may be rinsed by jettingor spraying water thereto in the space above the upper layer after thecleaning object is pulled up from the upper layer. In this case, forexample, by rinsing the machine and precision parts with rinsing waterjetted or sprayed from 1 or more outlets, normally 1 to 20 outlets(nozzles) (2) arranged above the surface of the water phase in thecleaning vessel, satisfactory rinsing can be achieved even at low waterphase depths. This makes it possible to reduce the size of the entirecleaning apparatus. The rinsing water used for this purpose may be anyone of pure water, tap water, circulated water, and water recycled fromthe water phase by a recycle treatment devise (4) such as an oil-waterseparator using activated charcoal, membrane, or vaporization. Wherenecessary, the lower layer oil phase can be jetted from such nozzles,while being circulated using a pump.

The cleaning vessel used may be of the single-vessel type or themultiple-vessel type; in the latter case, a number of cleaning vesselsbased on the same cleaning method are used. Where necessary, thecleaning vessel may be used in combination with a conventional cleaningmethod in common use. The in-line method, in which the cleaning objectis continuously cleaned, while being transported using a belt conveyoretc., or the barrel method may be used. The present invention isapplicable to all known cleaning methods.

The cleaning process of the present invention can be used for cleaningsolid surfaces of glass, ceramic, metals, plastics, etc. The cleaningprocess of the present invention is especially effective for cleaningmachine parts, electrical parts, precision parts and machine tools whichare used for assembling and processing these parts. Here, examples ofthe precision parts include electronic parts, electrical parts,precision instrument parts, formed resin parts, optical parts and thelike. Illustrative examples of the electronic parts include printedwiring boards for use in electronics-aided instruments such as computersand peripheral devices thereof, domestic electrical instruments,communications instruments, OA instruments and the like; hoop materialsfor use in contact parts such as IC lead frames, resistors, condensers,relays and the like; liquid crystal displays for use in OA instruments,clocks, computers, toys, domestic electrical instruments and the like;magnetic recording parts for use in recording/reproduction of image orsound and related parts thereof; semi-conductor materials such assilicon or ceramic wafers and the like; parts for electrostriction usesuch as quarts oscillators and the like; and photoelectric transferparts for use in CD, PD, copying instruments, optical recordinginstruments and the like. Illustrative examples of the electrical partsinclude motor parts such as a brush, a rotor, a stator, a housing andthe like; ticket delivery parts for use in vending machines and variousother instruments; and coin-checking parts for use in vending machines,cash dispensers and the like. Illustrative examples of the precisioninstrument parts include bearings for use in precision drivers, videorecorders and the like; and parts for processing use such as super hardtips and the like. Illustrative examples of the formed resin partsinclude precision resin parts for use in cameras, cars and the like.Illustrative examples of the optical parts include lenses for use incameras, eyeglasses, optical instruments and the like, in addition toother related parts such as spectacle rims, clock housings, watch bandsand the like. Illustrative examples of the machine parts include gears,camshaft springs, shafts, bearings, and other parts used in automobileengines and actuators. Illustrative examples of the electrical partsinclude motors, e.g. those used in video players, plastic products,electron guns, and shadow masks. Illustrative examples of the machinetools include those which are used in respective steps formanufacturing, molding, processing, assembling, finishing and the likeof the precision parts described above, as well as various types ofinstruments and parts thereof that are used for the handling ofprecision parts.

Though the cleaning process of the present invention is usefulespecially for cleaning flux-stained printed wiring boards, crystallineliquid-stained glass substrates and the like, the inventive cleaningprocess can be applied to any type of machine and precision parts aslong as these parts have solid surfaces stained with various types ofworking oils, fluxes and the like which may interfere the latertreatments in assembling and processing steps, or with various types ofoily foul substances which may deteriorate the characteristic propertiesof the final products. The cleaning process of the present inventionexerts its characteristic effect especially when the foul substances aremainly organic oily substances such as fats and oils, machine oils,quenching oils, cutting oils, greases, liquid crystals, rosin-basedfluxes and the like. Such foul substances can be removed effectivelyeven when they are contaminated with metal powders, inorganic powdersand the like, because these powders are removed together with removal ofthe organic oily substances.

The present invention is hereinafter described in more detail by meansof the following working examples and comparative examples, but is notlimited by these examples. The cloud points shown in the Examples weredetermined as a temperature at which a 1% by weight aqueous sampleliquid (deionized water used) became cloudy.

EXAMPLES 1 THROUGH 9 AND COMPARATIVE EXAMPLES 1 THROUGH 3

Cleaning liquids comprising the compositions shown in Table 1 areprepared. Each liquid is diluted with deionized water to organicsubstance content of 50% by weight. Seven liters of this dilution isplaced in a cleaning apparatus (cleaning vessel illustrated in FIG. 1)having a 10-liter capacity and equipped with an ultrasonic oscillatorand mechanical stirrer, and is kept standing for 30 minutes at atemperature set between 20° and 100° C. (30° C. for Examples 2, 5, 6 and7; 80° C. for Example 4; 70° C. for Examples 8 and 9; 50° C. for theother Examples).

Thirty minutes later, samples are taken from the surface of the cleaningliquid and lower layers in the cleaning vessel. The organic substancecontent in the cleaning liquid is determined from the TOC value(Shimadzu TOC-500 used) to calculate the separation rate.

In Examples 1 through 9, it is shown that at given temperatures between20° and 100° C., not less than 50% by weight of the organic substancescontained are separated from the aqueous liquid, resulting in theformation of a water phase in the upper layer and an oil phasecomprising dense organic substance liquid in the lower layer.Correspondingly, the organic substance odor generated from the cleaningliquid decreases markedly after phase separation.

On the other hand, in Comparative Example 1, although 85% by weight ofthe organic substances are separated from the aqueous liquid at 50° C.,stronger odor is generated after phase separation, because an oil phaseis formed in the upper layer, and a water phase in the lower layer. Theupper layer oil phase in Comparative Example 1 has a flashing point of71° C. In Comparative Example 2, an oil phase is formed as a thin upperlayer, and a water phase as the lower layer, with stronger odorgenerated after phase separation. In Comparative Example 3, the cleaningliquid used is the same as in Example 1.

Next, the following test materials are cleaned using the above cleaningliquid after being kept standing for 30 minutes. 1) Test material 1: asteel test piece (10 cm×15 cm), coated (10 g/m²) with a naphthenemineral oil (40° C., 350 cst), 2) test material 2: a glass substrate (10cm×10 cm), coated (5 g/m²) with a liquid crystal, and 3) test material3: a printed board (10 cm×15 cm), treated with a rosin flux. Duringcleaning, each test piece is kept in fully contact with the oil phase,except that in Comparative Example 3; the test piece is cleaned in theabsence of phase separation by stirring the entire cleaning liquid.

Cleaning is performed at a temperature of 50° C. in the lower layer for0.5 minutes under ultrasonication conditions. The test piece is thentransferred to the upper layer and ultrasonically rinsed for 0.5minutes, after which it is taken out from the cleaning vessel and driedat 80° C. for 15 minutes. The cleaning performance of the cleaningliquid, determined on the basis of the test piece weight change notedafter cleaning, is expressed using the following equation: ##EQU1##wherein I stands for weight of test piece before cleaning; II stands forweight of test piece after cleaning; and III stands for weight ofuntreated test piece.

The obtained values are evaluated using the following 4-grade rating:

≧90: ⊚ (excellent)

75-89: ∘ (good)

60-74: Δ (fair)

<60: x (poor)

                                      TABLE 1                                     __________________________________________________________________________                         Cloud                                                                         Point                                                                             Examples                   Comparative Examples      Detergent Composition & Evaluation Items                                                           (°C.)                                                                      1  2  3  4  5  6  7  8  9  1  2   3                  __________________________________________________________________________    Components                                                                          Dibenzyl ether 10>                   89       20     95                 & Amounts                                                                           Phenol (EO).sub.3                                                                            35  95       25    20                                    (% by Benzyl alcohol (EO).sub.1                                                                    10>    60             3                                  weight)                                                                             Benzyl alcohol (PO).sub.2                                                                    10>          35 70                                             Benzyl alcohol 10>    10                                                      Styrenated phenol (EO).sub.4                                                                 10>          25                                                (PO).sub.10 (EO).sub.4                                                                       10>       65                                                   Phenol (PO).sub.5 (EO).sub.2                                                                 10>    30                                                      Phenyl ethyl acetal                                                                          10>       30                                                   Butyl alcohol (EO).sub.2                                                                     100<            30    5           70                           Octyl alcohol (EO).sub.4                                                                     10>                 5                                          Paraffin (Av. number of carbon                                                               10>                            65 10                           atoms = 10)                                                                   Dibutyl phthalate                                                                            10>                76                                          Diethanolamine 100<       1          1   5                                    Oleyl alcohol (EO).sub.10                                                                    58   5       15       2      5 15 10   5                       Sodium dodecylbenzenesulfonate                                                               100<                              10                           Chlorophenol (EO).sub.4                                                                      53                       95 25                                 p-Chloroacetophenone                                                                         10>                         45                                 Methyl o-bromobenzoate                                                                       10>                         25                           Cloud Point(°C.) of the compositions                                                            38  10>                                                                              10>                                                                             15  10>                                                                              10>                                                                             10>                                                                              54  10>                                                                              10>                                                                             100<                                                                              38                 Separation                                                                          TOC in lower layer/(TOC in                                                                       95 98 83 91 68 90 87 96 97 15 45  95                 Ratio (%)                                                                           lower layer + TOC in upper layer) × 100                           Odor of                                                                             Before phase separation                                                                          B  B  B  B  B  B  B  C  C  B  B   B                  Cleaning                                                                            After phase separation                                                                           D  D  D  D  C  C  D  D  D  A  B   D                  Liquid                                                                        Cleaning                                                                            Ultrasonic cleaning after 30-minutes standing                                                    ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ◯˜⊚                                             ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 X˜Δ                                                                  Δ                                                                           --                 Performance                                                                         Ultrasonic cleaning with stirring                                                                -- -- -- -- -- -- -- -- -- -- --  Δ˜.                                                               largecircle.       __________________________________________________________________________     (EO).sub.n : Ethylene oxide adduct (PO).sub.n : Propylene oxide adduct n:     Average molar addition No. A: Extremely strong B: Strong C: Medium D:         Slight                                                                   

In Examples 1 through 9, a good cleaning performance is obtained. InComparative Example 1, no satisfactory cleaning performance is obtained,because a large amount of the surface layer oil phase is adhered to thetest piece, when the test piece is pulled up from the cleaning liquid.In Comparative Example 2, the cleaning performance was insufficient,because the oil phase, a dense organic substance phase, does not formsmoothly. In Comparative Example 3, the cleaning performance lowers,despite the use of the same cleaning liquid as in Example 1, because theentire cleaning liquid is uniformly stirred using a mechanical stirrerduring the cleaning test.

Also, in Examples 1 through 9, when the test piece is rinsed for 0.5minutes by jetting water recycled from the water phase with a recycletreatment devise at a pressure of 1 kg/cm², after being pulled out fromthe water phase and before drying, the cleaning performance increases bya factor of 1.5 to 5, in comparison with the absence of this operation.

INDUSTRIAL APPLICABILITY

According to the cleaning process of the present invention, the risk offire, explosion, etc. following flashing, and workplace environmentalpollution, such as odor generation, due to organic substancevolatilization, are prevented, because the upper layer of the cleaningliquid is constantly a water phase. Moreover, a high cleaningperformance against various liquid or solid organic stains is ensured,because the dense detergent liquid forming an oil phase as the lowerlayer serves for cleaning. As a result, a good cleaning effect is alsoobtained against inorganic stains, such as wear dusts, which are presentalong with organic stains.

I claim:
 1. A process for cleaning a cleaning object, comprising thesteps of:placing water and organic substances containing a nonionicsurfactant composition having a cloud point of not higher than 100° C.in a ratio of not less than 30% by weight, with or without previousblending, in a cleaning vessel, wherein the organic substances have aspecific gravity higher than that of water and, when mixed with water,placed in the cleaning vessel and kept standing at a temperature of from20° to 100° C. for 30 minutes, exhibit phase separation such that notless than 50% by weight of the organic substances is separated into alower layer; maintaining a temperature above the cloud point of thenonionic surfactant, thereby allowing water and the organic substancesto be in the state of phase separation in which the concentration of theorganic substances in a lower layer is higher than that in an upperlayer; and cleaning the cleaning object in the lower layer.
 2. Theprocess according to claim 1, wherein ultrasonic wave, stirring orin-liquid jetting is applied to the upper and/or lower layers.
 3. Theprocess according to claim 1, wherein the cleaning object is pulled upfrom the upper layer and then rinsed by jetting or spraying water in aspace above the upper layer.
 4. The process according to claim 1,wherein 80 to 99.9% by weight of the organic substances is separatedinto the lower layer.
 5. The process according to claim 1, wherein theorganic substances further comprise one or more aromatic hydrocarboncompounds, esters having an aromatic hydrocarbon group, ethers having anaromatic hydrocarbon group, alcohols having an aromatic hydrocarbongroup or ketones having an aromatic hydrocarbon group.
 6. The processaccording to claim 1, wherein the nonionic surfactant having a cloudpoint of not higher than 100° C. is a compound represented by theformula:

    R.sub.1 X(AO).sub.m R.sub.2 or R.sub.1 X(AO).sub.n YR.sub.2

wherein R₁ represents a hydrocarbon group having 6 to 18 carbon atomsthat may have a substituent and that has at least one aromatic ring; R₂represents a hydrogen atom or a hydrocarbon group having 1 to 10 carbonatoms that may have a substituent; X represents an ether group, an estergroup or an amino group; Y represents an ether group or an ester group;(AO) represents an alkylene oxide having 2 to 4 carbon atoms; m and neach is an average molar addition number of (AO), m being 0 to 20 and nbeing 1 to
 20. 7. The process according to claim 1, further comprisingthe step of rinsing the cleaning object in the upper layer.
 8. Theprocess according to claim 2, wherein the cleaning object is pulled upfrom the upper layer and then rinsed by jetting or spraying water in aspace above the upper layer.
 9. The process according to claim 2,further comprising the step of rinsing the cleaning object in the upperlayer.
 10. The process according to claim 3, further comprising the stepof rinsing the cleaning object in the upper layer.
 11. The processaccording to claim 4, further comprising the step of rinsing thecleaning object in the upper layer.
 12. The process according to claim5, further comprising the step of rinsing the cleaning object in theupper layer.
 13. The process according to claim 6, further comprisingthe step of rinsing the cleaning object in the upper layer.